Lesson 12 (ICND 1 1.9) Describe the components required for network and Internet communications

This is a pretty vague objective and could encompass any number of hardware or software items.  For now we will stick with the basics. A lot of this will be review from Lesson 1 as there is a lot of overlap.  Feel free to visit lesson 1 again for review.

To communicate on a network you first need an originating host.  That host can be a laptop, a desktop, a tablet, a smart phone, an IP phone, a server, or any number of devices with an internet protocol (TCP/IP) address.

Next, you'll need a destination host to communicate with.  That destination host may be a web server in Singapore, the file server in your datacenter, or a laptop in the cubicle next to you.

For that host to communicate on the network to reach this intended destination, you'll need to have a communications medium, that medium can be 802.11 wireless, 3G or 4G cellular networks,  and copper or optical wired ethernet.

Local communications typically will remain on the local area network (LAN) comprised of switches, distant locations will typically require a WAN connection comprised of routers.

If you are looking to get to a destination on the public Internet, you will need to go through a default gateway.  A default gateway is the router closest to you.  It is literally the gateway you must go through to get to the outside.

There may be any number of routers and communications mediums between your local host and the destination.

Here's a video that explains the overall process.Again, this objective has a lot of overlap with Lesson 1, so it's mostly a review.  Many of the blanks will be filled in subsequent videos.

courtesy of http://www.datacenterscanada.com

Lesson 11 (ICND1 1.8) Determine the path between two hosts across a network

When you are asked to determine a path between two hosts in a network, you will most often accomplish this through the traceroute command.

Here's a great video by Cbtnuggets which explains traceroute in detail.

Lesson 10 ICND1(1.7) Interpret network diagrams

This is pretty much already been covered, but I'm going to post a couple interesting tidbits on the subject.

Here's a video on how to create a simple network diagram using Microsoft Visio created by OfficeOnlineVideos.  You can download a trial version of MS Visio.

Go to the below the Networkworld website, and check out the section Interpreting a Network Diagram.
 http://www.networkworld.com/subnets/cisco/053008-ch1-ccna-prep-library.html

The below diagram is referenced:
 http://www.networkworld.com/subnets/cisco/chapters/1587054620/graphics/01fig03.jpg

You should fully understand what is going on in this graphic from previous lessons.  If you have any questions, please post a comment.

Lesson 9 - ICND1(1.6c)Describe the impact of applications such as Voice Over IP on a network

In networking, bandwidth is the amount of data (expressed in bits per second) that can be transmitted within a certain unit of time (i.e. 1000Mbps, 100Mbps, 10Mbps, 28.8Kbps over a physical medium.  

Note: Bandwidth is often confused with throughput.  Throughput is the measurement of of actual network traffic traversing a network. So think of bandwidth as the potential of a connection, and throughput as the reality.  This is often confused by retail internet customers, who buy a 6Mbps DSL link, and complain when they download a file at 100Kbps.  While their bandwidth to the service provider is 6Mbps, the throughput to the destination file server (from end to end over the Internet) is only 100Kbps.

The below graphic is a general idea of bandwidth requirements.  Requirements can vary depending on the application used.

Lesson 9 - ICND1(1.6b)Describe the impact of applications such as Voice Over IP on a network

The second concept I will describe is delay.  Delay (also called latency) is how long a packet takes to get to it's destination.  If you think of a packet as a car driving down the highway, it's latency is how long it takes to get from home to the destination.  

Latency is typically measured in milliseconds.  Ethernet connections are considered low latency (a few milliseconds), while a satellite link is considered high latency (hundreds of milliseconds).  There are many factors which can affect latency.

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The next concept covered is loss.  Loss is the dropping of packets in transit. As you can see below, there is no middle ground for packet loss, it's either very bad or not so bad.  The reason why mission critical data transfers have a low sensitivity to packet loss, is that the upper layers are supposed recognize the loss and request a retransmission.  That being said, a high number of retransmissions will result in data transfers taking a significantly longer amount of time.  In video or audio applications, the audio or video stream will drop off intermittently as packets are loss.

Lesson 8 - ICND1(1.6a)Describe the impact of applications such as Voice Over IP on a network

When we talk about the impact of applications on a network, we are talking about Quality of Service (QoS).  According to TCP/IP Guide:

"The generic term quality of service describe the characteristics of how data is transmitted between devices"

Most people when they think about quality of service, they describe whether the Internet or applications are fast or slow, but it's really much more than this.

Check out the following video by DigitalSocietyOrg on Youtube.

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The QoS concept I will discuss first is jitter. Jitter is simply packets arriving at their destination at unpredictable rates, also defined as a variation in packet delay.  This can cause issues with real-time streaming applications such as voice or video.  It is often experienced as a skip or a chirp in the audio or video.  

Lesson 7 - ICND1(1.5b) Describe the purpose and basic operation of the protocols in the OSI and TCP models

Session Layer 5
Maps to TCP/IP Model Application Layer 

Examples: NetBIOS, RPC

Communication using Sessions.
Definition from TCP/IP Guide:

"As its name suggests, it is the layer intended to provide functions for establishing and managing sessions between software processes. Session layer technologies are often implemented as sets of software tools called application program interfaces (APIs), which provide a consistent set of services that allow programmers to develop networking applications without needing to worry about lower-level details of transport, addressing and delivery."

Presentation Layer 6
Maps to TCP/IP Model Application Layer 

Examples: Encryption, Compression, Translation

Communication using Data Formatting.
Definition from TCP/IP Guide: 

"Protocols at this layer take care of manipulation tasks that transform data from one representation to another, such as translation, compression and encryption. In many cases, no such functions are required in a particular networking stack; if so, there may not be any protocol active at layer six."

Application Layer 7
Maps to TCP/IP Model Application Layer 

Examples:Telnet, FTP, HTTP

Communication using User Input.